Selecting a coverage enhancement level based on signal strength measurement

ABSTRACT

Various communication systems may benefit from identification of and communication of coverage shortfall. For example, certain communication systems that employ machine type communication devices may benefit from having such shortfall communicated from the devices to a base station. For example, a method can include determining an amount of coverage shortfall of a device. The method can also include transmitting an indication of the amount of coverage shortfall.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to and claims the benefit and priority ofU.S. Provisional Patent Application No. 61/864,265, filed Aug. 9, 2013,the entirety of which is hereby incorporated herein by reference.

BACKGROUND

Field

Various communication systems may benefit from identification of andcommunication of coverage shortfall. For example, certain communicationsystems that employ machine type communication devices may benefit fromhaving such shortfall communicated from the devices to a base station.

Description of the Related Art

In long term evolution (LTE) release 12 (Rel-12) coverage improvementfor Machine Type Communications (MTC) may aim to extend LTE coverage 15dB beyond the typical range of LTE, defined by the LTE study item ascell-edge data rate of 20 kbps. Such an extension may allow LTE to beused for services such as smart metering, where the meters may beinstalled in basements or shielded locations and therefore subject tosubstantial penetration loss.

Conventionally, however, there is no appropriate mechanism(s) to supportscalability of spectral efficiency impact for coverage improvement byidentifying user equipment (UE) requiring additional coverageimprovement and informing eNB the amount of coverage the UE requires.Although the term user equipment is used herein, it should be broadlyunderstood to include all kinds of terminal devices including devicessuch as smart meters and sensors, which may not have conventional users.

FIG. 1 illustrates the RRC connection setup message sequence prior toestablishment of service. In general, the sooner the eNB is informed ofthe UE coverage shortfall, the better. Otherwise, all messages prior toacquiring this information may have to be transmitted with the maximumamount of redundancy or repetition. From FIG. 1, it can be seen thatthis information can be communicated by the UE using the random accesspreamble, radio resource control (RRC) connection request message, orRRC connection setup complete message.

User equipment (UEs) in coverage limited situations may transmit usingthe maximum power, for example, based on downlink (DL) path loss orafter power ramping. Thus, it can be hard for the eNB to accuratelydetermine the amount of coverage shortfall from uplink (UL) signal tointerference plus noise ratio (SINR) estimation. Instead, the UE is bestto determine this amount with respect to nominal cell coverage.

According to certain approaches, coverage shortfall may be transmittedon the physical random access channel (PRACH). This could be done, forexample, via preamble selection or having a specific PRACH tied to acoverage shortfall amount. Using the PRACH to send additionalinformation can substantially reduce the PRACH capacity. If the capacityof the PRACH is reduced, then more random access opportunities have tobe configured, leading to increased overhead. Furthermore, even if thePRACH can be used, it can only convey a limited amount of informationand may not be very efficient at doing so. For example, only a few bitsmay be possible and there may be neither coding nor cyclic redundancycheck (CRC) protection, so the information may be unreliable.

According to one approach, different PRACH configurations can be chosenby UEs based on the estimated path loss according to some predefined orbroadcasted rule. For example, different physical resources or differentpreamble sequence can indicate different ranges of path loss.

According to another approach, the number of PRACH repetitions can forexample be signaled from the UE to eNB implicitly through the UE'schoice of PRACH time/frequency/sequence resource. The mapping betweennumber of repetitions and resource could be given by the broadcastedPRACH configuration.

According to a further approach, PRACH may be used such that it caninform eNB the amount of coverage enhancement a low cost MTC UE needs.For example a pre-defined mapping can be used between PRACH resource andthe amount of necessary coverage enhancements.

According to an additional approach, the system or eNB can pre-setseveral path loss ranges, with each path loss range related to an amountof coverage enhancement and a specific resource for preambletransmission. When eNB successfully detects the preamble transmitted bythe UE on a specific resource, it can acquire the amount of coverageimprovement.

Also, a very limited information on path loss can be indicated towardsthe network if the RRC parameter messagePowerOffsetGroupB is configured.

SUMMARY

According to a first embodiment, a method can include determining anamount of coverage shortfall of a device. The method can also includetransmitting an indication of the amount of coverage shortfall.

In a variant, the amount can be a coarse amount.

In a variant, the transmitting can be contingent on a path loss of thedevice exceeding a first threshold path loss.

In a variant, the transmitting can be further contingent on the pathloss of the device not exceeding a second threshold path loss.

In a variant, the amount can be indicated by an mPRACH.

In a variant, the transmitting can include transmitting the mPRACHoverlapping a PRACH.

In a variant, the transmitting can be contingent on mPRACH being turnedon by a base station.

In a variant, a period of the mPRACH can be at least double a period ofthe PRACH.

In a variant, the transmitting the indication can include selecting apreamble format based on a coverage shortfall.

In a variant, the determining the coverage shortfall can includecomparing a path loss to a nominal path loss provided by a base station.

In a variant, the method can further include subsequently sending a fineamount of coverage shortfall in radio resource control signaling.

According to a second embodiment, a method can include preparing athreshold value associated with mPRACH. The method can also includebroadcasting the threshold value.

In a variant, the method can be performed by a base station.

In a variant, the method can further including turning on the mPRACH ata first time and turning off the mPRACH at a second time.

In a variant, the threshold value can be a minimum path loss to qualifyto use mPRACH.

In a variant, the method can further include broadcasting a secondthreshold value.

In a variant, the second threshold value can be a maximum path loss toqualify to use mPRACH.

In a variant, the method can include determining at least one of a PDCCHaggregation level or repetition factor based on a preamble selection inthe mPRACH.

In a variant, the method can include providing a nominal path lossvalue.

According to third and fourth embodiments, respectively, an apparatuscan include at least one processor and at least one memory includingcomputer program code. The at least one memory and the computer programcode can be configured to, with the at least one processor, cause theapparatus at least to perform a respective method according to the firstand second embodiments, in all their variants.

According to fifth and sixth embodiments, respectively, an apparatus caninclude means for performing a respective method according to the firstand second embodiments, in all their variants.

According to seventh and eighth embodiments, respectively, anon-transitory computer readable medium can be encoded with instructionsthat, when executed in hardware, perform a process. The process can be arespective method according to the first and second embodiments, in alltheir variants.

According to ninth and tenth embodiments, respectively, a computerprogram product can encode instructions for performing a process. Theprocess can be a respective method according to the first and secondembodiments, in all their variants.

According to eleventh and twelfth embodiments, respectively, a systemcan include the apparatuses of the third and fourth embodiments or theapparatus of the fifth and sixth embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

For proper understanding of the invention, reference should be made tothe accompanying drawings, wherein:

FIG. 1 illustrates an RRC connection setup message sequence.

FIG. 2 illustrates an example of mPRACH and PRACH allocation.

FIG. 3 illustrates an example of different repetition factors on mPRACH.

FIG. 4 illustrates path loss indicated as a phase difference between twosegments.

FIG. 5 illustrates a method according to certain embodiments.

FIG. 6 illustrates a system according to certain embodiments.

DETAILED DESCRIPTION

Certain embodiments provide a mechanism so that several coverageimprovement levels can be supported, for example 5 dB, 10 dB, and 15 dB.UEs can then be configured to use the appropriate amount of coverageimprovement, for example repetition factor or transmission time interval(TTI) bundling size, depending on the UE's coverage shortfall amount.

The term “coverage shortfall” can refer to a variety of issues, such asfailure to meet a coverage threshold, lack of resources, or lack ofsufficient power to transmit in the whole cell. In certain embodiments,the term “coverage shortfall” refers specifically to an amount ofadditional signal strength desired, or needed, by a UE from the evolvedNode B (eNB). For example, as will be discussed below, a UE that usesthe machine type communication PRACH can calculate its estimatedcoverage shortfall as the difference of a measured downlink (DL) pathloss and a threshold, dl-PathlossmPRACH.

Certain embodiments, for example, provide two PRACHs, a PRACH that canbe viewed as a normal PRACH and a machine type communication (MTC) PRACH(mPRACH), which may be used for extended coverage.

In certain embodiments, mPRACH can be used for coverage-limited UEs withnew PRACH format(s). The mPRACH can have a much longer period thanPRACH, in order to reduce overhead. The period of mPRACH can be tied toa number of coverage limited UEs and other factors.

The mPRACH can overlap PRACH. For example, the mPRACH may use a samefrequency resource as PRACH.

The mPRACH can be configurable by the eNB. For example, the mPRACH canbe turned ON or OFF by the eNB.

The eNB can broadcast a threshold dl-PathlossmPRACH associated withmPRACH. The UEs with path loss higher than this threshold can use mPRACHfor access. The eNB can also broadcast a second thresholddl-PathlossMaxmPRACH, where UEs with path loss higher than this valueare not allowed to connect to the system. One or more PRACH formats canbe supported within mPRACH.

The UE can communicate coarse amount of coverage shortfall using mPRACH.The coverage shortfall can be, for example, determined based ondl-PathlossExtendedPRACH.

The PDCCH aggregation level or repetition factor may be implicitlydetermined from the mPRACH preamble selection. For example, the UEs thatuse mPRACH can have supported control channel element (CCE) aggregationlevels of 16 or 32, or repetition factor of 2 or 4.

In an RRC connection request message, the UE can send either a refinedestimate, for example an additional estimate, or a more completeestimate of coverage shortfall amount, for example usingdl-CoverageExtensionAmount. Some unused bits in the message can berepurposed to communicate this information, or some information elementscan be reinterpreted to include this information.

In certain embodiments, the eNB can configure a UE to report newdl-CoverageExtensionAmount if DL PL changes by dl-PathlossCoverageChangeamount.

Thus, certain embodiments may provide a two-step method for informingthe eNB of the coverage shortfall: first a coarse amount can beindicated via mPRACH and then either refined/additional or completeamount can be indicated using an RRC connection request message.

Moreover, certain embodiments may employ broadcasting of the nominalcell coverage path loss by the eNB for UEs to determine the amount ofcoverage shortfall.

Furthermore, certain embodiments may use various methods for UEs tocommunicate the coverage shortfall in the mPRACH, as well as variousways to communicate coverage shortfall in the RRC connection requestmessage.

Structure and configuration of the mPRACH can be arranged in a varietyof ways, as discussed below. In certain embodiments, physical downlinkcontrol channel (PDCCH) aggregation level or repetition factor can beimplicitly tied to preamble selection in the mPRACH.

More particularly, according to certain embodiments two PRACH types aresupported within the system: a so-called normal PRACH and an mPRACH forextended coverage. The mPRACH can be used for coverage-limited UEs withnew PRACH format(s) and can overlap the PRACH. The mPRACH can extendover a much longer time than the PRACH, to allow for longer transmissionby coverage-limited UEs. Moreover, the mPRACH can repeat lessfrequently. An illustration of PRACH and mPRACH allocation is shown inFIGS. 2A and 2B where the PRACH occurs every other subframe while themPRACH occurs every eight subframes. On the other hand, the mPRACHcontinues for four subframes while the PRACH continues for just onesubframe. In FIG. 2A, the mPRACH is assigned distinct frequency resourcefrom the PRACH, while in FIG. 2B the mPRACH overlaps with the PRACH. Inthe illustrated embodiment, a subframe is one millisecond, althoughother lengths of subframes are permitted.

The period of the mPRACH can be configured based on many factors asdescribed below. For example, the period of mPRACH can be based on acell range extension amount, for example, by using a ratio of extendedcoverage area compared to nominal coverage area. Additionally, oralternatively, the period of mPRACH can be based on the number ofcoverage limited UEs expected in this cell. This number can be obtainedthrough, for example, cell planning, past historical values, or userfeedback. Additionally, or alternatively, the period of mPRACH can bebased on a multiple of the PRACH periodicity based on historical PRACHusage or load.

Possible values for mPRACH period may be standardized and valueselection, from amongst those possible values, may be made by the eNB inan implementation specific way.

In one embodiment, eNB can broadcast a threshold dl-PathlossmPRACHassociated with mPRACH. UEs with path loss higher than this can berequired by the eNB to use mPRACH for access.

In another embodiment, the eNB can additionally broadcast a secondthreshold dl-PathlossMaxmPRACH where UEs with path loss higher than thisis not allowed to connect to the system. This can be used, for example,to prevent high-path loss UEs that are able to read the systeminformation from trying to connect to the cell. It can also be used forload balancing when the system is too heavily loaded.

The parameter can be configured based on many factors. For example, theparameter can be based on a maximum supportable coverage improvement,for example a maximum repetition factor and/or power boosting. Theparameter can also or additionally be based on system load, for exampleno coverage improvement support beyond a certain load. The parameter canfurther be based on a maximum amount of resource that can be reservedfor MTC or for coverage improvement.

The UE using the mPRACH may not have to undergo a random access powercontrol procedure, as it may always be transmitting at the maximumpower. A UE that uses the mPRACH can calculate its estimated coverageshortfall as the difference of the measured DL path loss anddl-PathlossmPRACH. Subsequently, the UE can provide a coarse orquantized estimate of this value up to the eNB using one of severalmethods.

In one embodiment, the UE can use a different amount of repetitionfactors or transmission times as shown in FIG. 3. Coverage shortfall canbe given by how long the UE transmits. For instance, several preambleformats with fixed repetition factors can be predefined (for example, 4,8, 16, 32, and 64) and selected by the UE based on its coverageshortfall.

In one embodiment, the PRACH preamble can be made up of two segments asshown in FIG. 4. Each segment can have its own cyclic prefix and eachsegment can use the same root sequence and preamble index. The coverageshortfall can be indicated using the phase difference between twosegment sequences of a PRACH preamble to indicate the path loss. Forexample, the phase difference can be expressed as (x−min)/(max−min)*pi,limited to pi to avoid phase ambiguity. The terms max and min can be themaximum path loss and minimum path loss values broadcast by the eNB inthe system information block (SIB) message. The term x can be themeasured path loss at UE. In other words, the phase of [CP2 SEQ2] can berotated with respect to [CP1 SEQ1]. In this way, the path loss asobserved by UE can be fed back in an analog fashion. There can befurther optimizations, such as for example, a nonlinear/piece-wisemapping scheme from path loss to the phase difference can be used so thepath loss range(s) of interest to the network can get expanded range inthe phase difference, and the nonlinear mapping or piece-wise linearmapping can be used so that some path loss range is given more detailedrepresentation in the phase domain. For example, [−150 dBm and −100 dBm]can be mapped to [0.75]*pi, while [−100 dBm and −80 dBm] can be mappedto [0.75 to 1]*pi).

As for the corresponding PRACH receiver design, on the eNB side, twosegments can be power-combined to detect the preamble index. The phasedifference between two segments can be estimated at each preamble index.

In one embodiment, the coverage shortfall can be indicated by preambleor channel selection. In another embodiment, the coverage shortfall canbe indicated by modulation (for example, quadrature phase shift keying(QPSK)) on top of preamble to inform eNB of coverage enhancement amount(for example, 5, 10, or 15 dB), or via spreading code. In a furtherembodiment, the eNB can use different detection threshold at the eNB todistinguish different amount of coverage enhancement (for example, T1,T2, T3, or T4). This can be used to fine-tune the amount of coverageenhancement where UEs transmit with the same power and the samerepetition factor. This is possibly a complementary technique to otherapproaches, and can be combined with them.

Based on successfully detecting the preamble on the mPRACH, the eNB canhave some knowledge of the amount of coverage shortfall associated withthis UE. At this stage, however, only a coarse estimate may be neededfor the eNB to select the appropriate MCS and repetition factor for therandom access response message. The MCS and repetition factor may becommunicated using the DCI on the PDCCH. However, the PDCCH itself mayrequire a certain number of repetitions. Based on the preamble selectionfor the mPRACH, the UE may be able to implicitly determine the PDCCHrepetition factor. For example, UEs that use mPRACH can have supportedCCE aggregation levels of 16 or 32. Alternately, it may be configuredfor CCE aggregation level of 8 and repetition factor of 2 or 4.

In an RRC connection request message, the UE can send an additional orcomplete estimate of coverage shortfall amount to the eNB. This step maybe made optional if, for example, the mPRACH-based procedure can providesufficient information, such as, for example, through a flag on thesystem information broadcast. Alternatively, if random access capacityis a concern, the eNB may disable preamble selection on the mPRACH andrely solely on this estimate from the RRC connection request message.

In another embodiment, the information from the RRC connection requestmessage can be used to combine with information from the preamble toarrive at more complete information. For example, a coarse estimate canbe obtained via the mPRACH. Additional information can be sent in theRRC connection request message to get at a more refined shortfall level.For example, the complete information may be 3 bits obtained bycombining 1 bit from PRACH with 2 bits from the RRC connection requestmessage.

In another embodiment, information elements, spare bits, or randomvalues in the RRC connection request message can be reinterpreted tocommunicate the amount of coverage shortfall. For example, some valuesof the EstablishmentCause information element can be reinterpreted tocommunicate additional information about the amount of coverageshortfall.

After RRC connection has been established, the UE may retain thisinformation for an extended amount of time, for example in Small Dataand Device Triggering Enhancements (SDDTE), a method for keeping UE inconnected mode to reduce overhead may be employed. The eNB can configureUE to report the coverage shortfall if its DL PL changes bydl-PathlossCoverageChange amount, which may be equivalent to coverageshortfall changing by the same amount.

FIG. 5 illustrates a method according to certain embodiments. As shownin FIG. 5, a method can include, at 510, determining an amount ofcoverage shortfall of a device. The can also include, at 520,transmitting an indication of the amount of coverage shortfall. Theamount coverage shortfall can be indicated by an mPRACH.

The amount can be a coarse amount. For example, the coarse amount can beamount represented by one or two bits.

The transmitting can be contingent on a path loss of the deviceexceeding a first threshold path loss. Thus the method can include, at525, determining that the path loss exceeds the first threshold.Moreover, the transmitting can be further contingent on the path loss ofthe device not exceeding a second threshold path loss. Thus the methodcan include, at 527, determining that the path loss does not exceed thesecond threshold.

The transmitting the mPRACH can include transmitting the mPRACHoverlapping a PRACH, as illustrated in FIG. 2B and discussed above.

The transmitting can be contingent on mPRACH being turned on by a basestation. Thus, the method can include, as shown in FIG. 5 at 505,determining that mPRACH has been turned on.

A period of the mPRACH can be at least double a period of the PRACH, asillustrated in FIGS. 2A and 2B.

The transmitting the indication can include, at 523, selecting apreamble format based on a coverage shortfall.

The determining the coverage shortfall can include, at 515, comparing apath loss to a nominal path loss provided by a base station.

The method can further include, at 530, subsequently sending a fineamount of coverage shortfall in radio resource control signaling.

The above steps can be performed by, for example, any terminal device,such as a user equipment broadly including devices such as sensors andsmart meters in addition to devices like smart phones and personaldigital assistants. The following steps can be performed by a basestation, such as an evolved node B (eNB).

Thus, as shown in FIG. 5, the method can include, at 540, preparing athreshold value associated with mPRACH. The method can also include, at550, broadcasting the threshold value.

The method can further include, at 560, turning on the mPRACH at a firsttime and, at 565, turning off the mPRACH at a second time.

The threshold value can be a minimum path loss to qualify to use mPRACH.The method can further include, at 570, broadcasting a second thresholdvalue. The second threshold value can be a maximum path loss to qualifyto use mPRACH.

The method can include, at 580, determining at least one of a PDCCHaggregation level or repetition factor based on a preamble selection inthe mPRACH.

In a variant, the method can also include, at 590, providing a nominalpath loss value to the user equipment or similar device.

FIG. 6 illustrates a system according to certain embodiments of theinvention. In one embodiment, a system may include multiple devices,such as, for example, at least one UE 610, at least one eNB 620 or otherbase station or access point, and at least one core network element 630.In certain systems, only UE 610 and eNB 620 may be present, and in othersystems UE 610, eNB 620, and a plurality of other user equipment may bepresent. Other configurations are also possible.

Each of these devices may include at least one processor, respectivelyindicated as 614, 624, and 634. At least one memory can be provided ineach device, and indicated as 615, 625, and 635, respectively. Thememory may include computer program instructions or computer codecontained therein. The processors 614, 624, and 634 and memories 615,625, and 635, or a subset thereof, can be configured to provide meanscorresponding to the various blocks of FIG. 5.

As shown in FIG. 6, transceivers 616, 626, and 636 can be provided, andeach device may also include an antenna, respectively illustrated as617, 627, and 637. Other configurations of these devices, for example,may be provided. For example, core network element 630 may be configuredfor wired communication, rather than wireless communication, and in sucha case antenna 637 would illustrate any form of communication hardware,without requiring a conventional antenna.

Transceivers 616, 626, and 636 can each, independently, be atransmitter, a receiver, or both a transmitter and a receiver, or a unitor device that is configured both for transmission and reception.

Processors 614, 624, and 634 can be embodied by any computational ordata processing device, such as a central processing unit (CPU),application specific integrated circuit (ASIC), or comparable device.The processors can be implemented as a single controller, or a pluralityof controllers or processors.

Memories 615, 625, and 635 can independently be any suitable storagedevice, such as a non-transitory computer-readable medium. A hard diskdrive (HDD), random access memory (RAM), flash memory, or other suitablememory can be used. The memories can be combined on a single integratedcircuit as the processor, or may be separate from the one or moreprocessors. Furthermore, the computer program instructions stored in thememory and which may be processed by the processors can be any suitableform of computer program code, for example, a compiled or interpretedcomputer program written in any suitable programming language.

The memory and the computer program instructions can be configured, withthe processor for the particular device, to cause a hardware apparatussuch as UE 610, eNB 620, and core network element 630, to perform any ofthe processes described above (see, for example, FIG. 5). Therefore, incertain embodiments, a non-transitory computer-readable medium can beencoded with computer instructions that, when executed in hardware,perform a process such as one of the processes described herein.Alternatively, certain embodiments of the invention can be performedentirely in hardware.

Furthermore, although FIG. 6 illustrates a system including a UE, eNB,and core network element, embodiments of the invention may be applicableto other configurations, and configurations involving additionalelements. For example, not shown, additional UEs may be present.

Various embodiments may have various benefits or advantages. Forexample, certain embodiments provide for broadcasting of the nominalcell coverage path loss by the eNB, which may allow for accuratedetermination of the coverage shortfall using information alreadyavailable at the UE during access attempts, for example, DL path loss.

Moreover, coarse estimate (for example, 1 bit) of coverage shortfallsent on the mPRACH can allow higher capacity to be supported on themPRACH and for appropriate transmission of random access response.

Additional or complete estimate sent on the RRC connection setup messagecan allow coverage improvement to be tailored for individual UE, savingresources by using the appropriate level of coverage improvement. Alsosuch an approach may correct any error from mPRACH estimate.

Overhead saving may also be achieved by allowing mPRACH to overlap withPRACH, and by allowing eNB to also control the number ofcoverage-limited UEs attaching to the cell as well as the allowablecoverage improvement.

Certain embodiments may be applicable to systems relying on LTE Rel-12specifications. Other embodiments, however, can beimplementation-specific and can be done exclusively at the eNB.

One having ordinary skill in the art will readily understand that theinvention as discussed above may be practiced with steps in a differentorder, and/or with hardware elements in configurations which aredifferent than those which are disclosed. Therefore, although theinvention has been described based upon these preferred embodiments, itwould be apparent to those of skill in the art that certainmodifications, variations, and alternative constructions would beapparent, while remaining within the spirit and scope of the invention.

GLOSSARY

CCE Control Channel Element

CRC Cyclic Redundancy Check

DL Downlink

HARQ Hybrid Automatic Repeat Request

MIB Master Information Block

MTC Machine Type Communications

PHICH Physical HARQ Indicator Channel

PL Path Loss

PRACH Physical Random Access Channel

PUSCH Physical Uplink Shared Channel

QPSK Quadrature Phase Shift Keying

RRC Radio Resource Control

SIB System Information Block

SINR Signal to Interference plus Noise Ratio

SDDTE Small Data and Device Triggering Enhancements

TTI Transmission Time Interval

UE User Equipment

UL Uplink

We claim:
 1. A method, comprising: in a mobile device, receiving from abase station, information indicating support of a plurality of coverageenhancement levels for the mobile device, wherein a coverage enhancementlevel provides signal strength information and each coverage enhancementlevel corresponds to a different physical random access channel for themobile device; measuring downlink signal strength of the base station;selecting a coverage enhancement level from the plurality of coverageenhancement levels based on the downlink signal strength measurement ofthe base station; and transmitting a preamble signal, to the basestation, using a physical random access channel corresponding to theselected coverage enhancement level, wherein the physical random accesschannel corresponding to the selected coverage enhancement level is anextended physical random access channel overlapping a physical randomaccess channel.
 2. The method of claim 1, comprising determining anamount of coverage enhancement required by the mobile device from thebase station, related to the selected coverage enhancement level.
 3. Themethod of claim 2, comprising transmitting to the base station, anindication of the amount of coverage enhancement required by the mobiledevice.
 4. The method of claim 3, further comprising receiving from thebase station a random access response message having at least one of aphysical downlink control channel aggregation level or a repetitionfactor based on the transmitted indication of the amount of coverageenhancement.
 5. The method of claim 2, comprising selecting a preambleformat based on the amount of coverage enhancement required by themobile device.
 6. The method of claim 2, comprising determining theamount of coverage enhancement required by the mobile device bycomparing the downlink signal strength measurement of the base stationwith signal strength information associated with one or more of theplurality of coverage enhancement levels provided by the base station.7. The method of claim 1, wherein the selected coverage enhancementlevel is contingent on a path loss of the mobile device.
 8. The methodof claim 1, wherein a period of the extended physical random accesschannel is different from a period of the physical random access channelfor the mobile device.
 9. An apparatus, comprising: at least oneprocessor; and at least one memory including computer program code,wherein the at least one memory and the computer program code areconfigured to, with the at least one processor, cause the apparatus atleast to in a mobile device, receive from a base station, informationindicating support of a plurality of coverage enhancement levels for themobile device, wherein a coverage enhancement level provides signalstrength information and each coverage enhancement level corresponds toa different physical random access channel for the mobile device;measure downlink signal strength of the base station; select a coverageenhancement level from the plurality of coverage enhancement levelsbased on the downlink signal strength measurement of the base station;and transmit a preamble signal, to the base station, using a physicalrandom access channel corresponding to the selected coverage enhancementlevel, wherein the physical random access channel corresponding to theselected coverage enhancement level is an extended physical randomaccess channel overlapping a physical random access channel.
 10. Theapparatus of claim 9, wherein the at least one memory and the computerprogram code are configured to, with the at least one processor, causethe apparatus at least to determine an amount of coverage enhancementrequired by the mobile device from the base station, related to theselected coverage enhancement level.
 11. The apparatus of claim 10,wherein the at least one memory and the computer program code areconfigured to, with the at least one processor, cause the apparatus atleast to transmit to the base station an indication of the amount ofcoverage enhancement required by the mobile device.
 12. The apparatus ofclaim 10, wherein the selected coverage enhancement level is contingenton a path loss of the mobile device.
 13. The apparatus of claim 10,wherein the at least one memory and the computer program code areconfigured to, with the at least one processor, cause the apparatus atleast to select a preamble format based on the amount of coverageenhancement required by the mobile device.
 14. The apparatus of claim10, wherein the at least one memory and the computer program code areconfigured to, with the at least one processor, cause the apparatus atleast to determine the amount of coverage enhancement required by themobile device by comparing the downlink signal strength measurement ofthe base station with signal strength information associated with one ormore of the plurality of coverage enhancement levels.
 15. The apparatusof claim 9, wherein a period of the extended physical random accesschannel is different from a period of the physical random access channelfor the mobile device.
 16. A non-transitory computer readable medium,encoded with instructions that, when executed in hardware, cause thehardware to perform a process, the process comprising: in a mobiledevice, receiving from a base station, information indicating support ofa plurality of coverage enhancement levels for the mobile device,wherein a coverage enhancement level provides signal strengthinformation and each coverage enhancement level corresponds to adifferent physical random access channel for the mobile device;measuring downlink signal strength of the base station; selecting acoverage enhancement level from the plurality of coverage enhancementlevels based on the downlink signal strength measurement of the basestation; and transmitting a preamble signal, to the base station, usinga physical random access channel corresponding to the selected coverageenhancement level, wherein the physical random access channelcorresponding to the selected coverage enhancement level is an extendedphysical random access channel overlapping a physical random accesschannel.